The purpose of this proposal is to perform experiments in decerebrate cats to examine four specific aims: 1. To determine the neural input from the Kolliker-Fuse nucleus (KFN) to pharyngeal respiratory muscle motoneurons located in the hypoglossal nucleus (HGN). In addition, to neural pathways, neuromediator activity of the KLN will be explored. 2. To determine the effect of airway length on the mechanical effects of pharyngeal constrictor muscle contraction. It is hypoothesized that upper airway shortening may alter the mechanical effect of contraction of these muscles, such that they will have dilatory instead of constricting action. 3. To determine the effect of vagal afferent activity on pharyngeal muscle constrictor action. It is proposed that the pharyngeal muscles that are usually pharyngeal constrictors may become dilator muscles during hypercapnia in the absence of afferent vagal feedback. 4. To determine the changes in regional structure during contracture of various pharyngeal muscles by the use of retrograde fiberoptic imaging in a closed upper airway. This work is an expansion of work conducted to date by the PI, who has recently relocated to the University of Pennsylvania.